Optical bandpass filters which transmit a specific waveband of light have found wide application in a number of optical systems.
Optical bandpass filters constructed from waveguide grating routers—while offering useful narrow bandpass characteristics—are somewhat bulky, difficult to fabricate and consequently expensive.
Optical bandpass filters constructed from an all-pass filter and Mach-Zehnder structures are oftentimes too-sensitive to waveguide loss.